mm/kfence/report.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * KFENCE reporting.
   4  *
   5  * Copyright (C) 2020, Google LLC.
   6  */
   7
   8 #include <linux/stdarg.h>
   9
  10 #include <linux/kernel.h>
  11 #include <linux/lockdep.h>
  12 #include <linux/math.h>
  13 #include <linux/printk.h>
  14 #include <linux/sched/debug.h>
  15 #include <linux/seq_file.h>
  16 #include <linux/stacktrace.h>
  17 #include <linux/string.h>
  18 #include <trace/events/error_report.h>
  19
  20 #include <asm/kfence.h>
  21
  22 #include "kfence.h"
  23
  24 /* May be overridden by <asm/kfence.h>. */
  25 #ifndef ARCH_FUNC_PREFIX
  26 #define ARCH_FUNC_PREFIX ""
  27 #endif
  28
  29 extern bool no_hash_pointers;
  30
  31 /* Helper function to either print to a seq_file or to console. */
  32 __printf(2, 3)
  33 static void seq_con_printf(struct seq_file *seq, const char *fmt, ...)
  34 {
  35         va_list args;
  36
  37         va_start(args, fmt);
  38         if (seq)
  39                 seq_vprintf(seq, fmt, args);
  40         else
  41                 vprintk(fmt, args);
  42         va_end(args);
  43 }
  44
  45 /*
  46  * Get the number of stack entries to skip to get out of MM internals. @type is
  47  * optional, and if set to NULL, assumes an allocation or free stack.
  48  */
  49 static int get_stack_skipnr(const unsigned long stack_entries[], int num_entries,
  50                             const enum kfence_error_type *type)
  51 {
  52         char buf[64];
  53         int skipnr, fallback = 0;
  54
  55         if (type) {
  56                 /* Depending on error type, find different stack entries. */
  57                 switch (*type) {
  58                 case KFENCE_ERROR_UAF:
  59                 case KFENCE_ERROR_OOB:
  60                 case KFENCE_ERROR_INVALID:
  61                         /*
  62                          * kfence_handle_page_fault() may be called with pt_regs
  63                          * set to NULL; in that case we'll simply show the full
  64                          * stack trace.
  65                          */
  66                         return 0;
  67                 case KFENCE_ERROR_CORRUPTION:
  68                 case KFENCE_ERROR_INVALID_FREE:
  69                         break;
  70                 }
  71         }
  72
  73         for (skipnr = 0; skipnr < num_entries; skipnr++) {
  74                 int len = scnprintf(buf, sizeof(buf), "%ps", (void *)stack_entries[skipnr]);
  75
  76                 if (str_has_prefix(buf, ARCH_FUNC_PREFIX "kfence_") ||
  77                     str_has_prefix(buf, ARCH_FUNC_PREFIX "__kfence_") ||
  78                     !strncmp(buf, ARCH_FUNC_PREFIX "__slab_free", len)) {
  79                         /*
  80                          * In case of tail calls from any of the below
  81                          * to any of the above.
  82                          */
  83                         fallback = skipnr + 1;
  84                 }
  85
  86                 /* Also the *_bulk() variants by only checking prefixes. */
  87                 if (str_has_prefix(buf, ARCH_FUNC_PREFIX "kfree") ||
  88                     str_has_prefix(buf, ARCH_FUNC_PREFIX "kmem_cache_free") ||
  89                     str_has_prefix(buf, ARCH_FUNC_PREFIX "__kmem_cache_free") ||
  90                     str_has_prefix(buf, ARCH_FUNC_PREFIX "__kmalloc") ||
  91                     str_has_prefix(buf, ARCH_FUNC_PREFIX "kmem_cache_alloc"))
  92                         goto found;
  93         }
  94         if (fallback < num_entries)
  95                 return fallback;
  96 found:
  97         skipnr++;
  98         return skipnr < num_entries ? skipnr : 0;
  99 }
 100
 101 static void kfence_print_stack(struct seq_file *seq, const struct kfence_metadata *meta,
 102                                bool show_alloc)
 103 {
 104         const struct kfence_track *track = show_alloc ? &meta->alloc_track : &meta->free_track;
 105         u64 ts_sec = track->ts_nsec;
 106         unsigned long rem_nsec = do_div(ts_sec, NSEC_PER_SEC);
 107
 108         /* Timestamp matches printk timestamp format. */
 109         seq_con_printf(seq, "%s by task %d on cpu %d at %lu.%06lus:\n",
 110                        show_alloc ? "allocated" : "freed", track->pid,
 111                        track->cpu, (unsigned long)ts_sec, rem_nsec / 1000);
 112
 113         if (track->num_stack_entries) {
 114                 /* Skip allocation/free internals stack. */
 115                 int i = get_stack_skipnr(track->stack_entries, track->num_stack_entries, NULL);
 116
 117                 /* stack_trace_seq_print() does not exist; open code our own. */
 118                 for (; i < track->num_stack_entries; i++)
 119                         seq_con_printf(seq, " %pS\n", (void *)track->stack_entries[i]);
 120         } else {
 121                 seq_con_printf(seq, " no %s stack\n", show_alloc ? "allocation" : "deallocation");
 122         }
 123 }
 124
 125 void kfence_print_object(struct seq_file *seq, const struct kfence_metadata *meta)
 126 {
 127         const int size = abs(meta->size);
 128         const unsigned long start = meta->addr;
 129         const struct kmem_cache *const cache = meta->cache;
 130
 131         lockdep_assert_held(&meta->lock);
 132
 133         if (meta->state == KFENCE_OBJECT_UNUSED) {
 134                 seq_con_printf(seq, "kfence-#%td unused\n", meta - kfence_metadata);
 135                 return;
 136         }
 137
 138         seq_con_printf(seq, "kfence-#%td: 0x%p-0x%p, size=%d, cache=%s\n\n",
 139                        meta - kfence_metadata, (void *)start, (void *)(start + size - 1),
 140                        size, (cache && cache->name) ? cache->name : "<destroyed>");
 141
 142         kfence_print_stack(seq, meta, true);
 143
 144         if (meta->state == KFENCE_OBJECT_FREED) {
 145                 seq_con_printf(seq, "\n");
 146                 kfence_print_stack(seq, meta, false);
 147         }
 148 }
 149
 150 /*
 151  * Show bytes at @addr that are different from the expected canary values, up to
 152  * @max_bytes.
 153  */
 154 static void print_diff_canary(unsigned long address, size_t bytes_to_show,
 155                               const struct kfence_metadata *meta)
 156 {
 157         const unsigned long show_until_addr = address + bytes_to_show;
 158         const u8 *cur, *end;
 159
 160         /* Do not show contents of object nor read into following guard page. */
 161         end = (const u8 *)(address < meta->addr ? min(show_until_addr, meta->addr)
 162                                                 : min(show_until_addr, PAGE_ALIGN(address)));
 163
 164         pr_cont("[");
 165         for (cur = (const u8 *)address; cur < end; cur++) {
 166                 if (*cur == KFENCE_CANARY_PATTERN(cur))
 167                         pr_cont(" .");
 168                 else if (no_hash_pointers)
 169                         pr_cont(" 0x%02x", *cur);
 170                 else /* Do not leak kernel memory in non-debug builds. */
 171                         pr_cont(" !");
 172         }
 173         pr_cont(" ]");
 174 }
 175
 176 static const char *get_access_type(bool is_write)
 177 {
 178         return is_write ? "write" : "read";
 179 }
 180
 181 void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *regs,
 182                          const struct kfence_metadata *meta, enum kfence_error_type type)
 183 {
 184         unsigned long stack_entries[KFENCE_STACK_DEPTH] = { 0 };
 185         const ptrdiff_t object_index = meta ? meta - kfence_metadata : -1;
 186         int num_stack_entries;
 187         int skipnr = 0;
 188
 189         if (regs) {
 190                 num_stack_entries = stack_trace_save_regs(regs, stack_entries, KFENCE_STACK_DEPTH, 0);
 191         } else {
 192                 num_stack_entries = stack_trace_save(stack_entries, KFENCE_STACK_DEPTH, 1);
 193                 skipnr = get_stack_skipnr(stack_entries, num_stack_entries, &type);
 194         }
 195
 196         /* Require non-NULL meta, except if KFENCE_ERROR_INVALID. */
 197         if (WARN_ON(type != KFENCE_ERROR_INVALID && !meta))
 198                 return;
 199
 200         if (meta)
 201                 lockdep_assert_held(&meta->lock);
 202         /*
 203          * Because we may generate reports in printk-unfriendly parts of the
 204          * kernel, such as scheduler code, the use of printk() could deadlock.
 205          * Until such time that all printing code here is safe in all parts of
 206          * the kernel, accept the risk, and just get our message out (given the
 207          * system might already behave unpredictably due to the memory error).
 208          * As such, also disable lockdep to hide warnings, and avoid disabling
 209          * lockdep for the rest of the kernel.
 210          */
 211         lockdep_off();
 212
 213         pr_err("==================================================================\n");
 214         /* Print report header. */
 215         switch (type) {
 216         case KFENCE_ERROR_OOB: {
 217                 const bool left_of_object = address < meta->addr;
 218
 219                 pr_err("BUG: KFENCE: out-of-bounds %s in %pS\n\n", get_access_type(is_write),
 220                        (void *)stack_entries[skipnr]);
 221                 pr_err("Out-of-bounds %s at 0x%p (%luB %s of kfence-#%td):\n",
 222                        get_access_type(is_write), (void *)address,
 223                        left_of_object ? meta->addr - address : address - meta->addr,
 224                        left_of_object ? "left" : "right", object_index);
 225                 break;
 226         }
 227         case KFENCE_ERROR_UAF:
 228                 pr_err("BUG: KFENCE: use-after-free %s in %pS\n\n", get_access_type(is_write),
 229                        (void *)stack_entries[skipnr]);
 230                 pr_err("Use-after-free %s at 0x%p (in kfence-#%td):\n",
 231                        get_access_type(is_write), (void *)address, object_index);
 232                 break;
 233         case KFENCE_ERROR_CORRUPTION:
 234                 pr_err("BUG: KFENCE: memory corruption in %pS\n\n", (void *)stack_entries[skipnr]);
 235                 pr_err("Corrupted memory at 0x%p ", (void *)address);
 236                 print_diff_canary(address, 16, meta);
 237                 pr_cont(" (in kfence-#%td):\n", object_index);
 238                 break;
 239         case KFENCE_ERROR_INVALID:
 240                 pr_err("BUG: KFENCE: invalid %s in %pS\n\n", get_access_type(is_write),
 241                        (void *)stack_entries[skipnr]);
 242                 pr_err("Invalid %s at 0x%p:\n", get_access_type(is_write),
 243                        (void *)address);
 244                 break;
 245         case KFENCE_ERROR_INVALID_FREE:
 246                 pr_err("BUG: KFENCE: invalid free in %pS\n\n", (void *)stack_entries[skipnr]);
 247                 pr_err("Invalid free of 0x%p (in kfence-#%td):\n", (void *)address,
 248                        object_index);
 249                 break;
 250         }
 251
 252         /* Print stack trace and object info. */
 253         stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr, 0);
 254
 255         if (meta) {
 256                 pr_err("\n");
 257                 kfence_print_object(NULL, meta);
 258         }
 259
 260         /* Print report footer. */
 261         pr_err("\n");
 262         if (no_hash_pointers && regs)
 263                 show_regs(regs);
 264         else
 265                 dump_stack_print_info(KERN_ERR);
 266         trace_error_report_end(ERROR_DETECTOR_KFENCE, address);
 267         pr_err("==================================================================\n");
 268
 269         lockdep_on();
 270
 271         if (panic_on_warn)
 272                 panic("panic_on_warn set ...\n");
 273
 274         /* We encountered a memory safety error, taint the kernel! */
 275         add_taint(TAINT_BAD_PAGE, LOCKDEP_STILL_OK);
 276 }
 277
 278 #ifdef CONFIG_PRINTK
 279 static void kfence_to_kp_stack(const struct kfence_track *track, void **kp_stack)
 280 {
 281         int i, j;
 282
 283         i = get_stack_skipnr(track->stack_entries, track->num_stack_entries, NULL);
 284         for (j = 0; i < track->num_stack_entries && j < KS_ADDRS_COUNT; ++i, ++j)
 285                 kp_stack[j] = (void *)track->stack_entries[i];
 286         if (j < KS_ADDRS_COUNT)
 287                 kp_stack[j] = NULL;
 288 }
 289
 290 bool __kfence_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab)
 291 {
 292         struct kfence_metadata *meta = addr_to_metadata((unsigned long)object);
 293         unsigned long flags;
 294
 295         if (!meta)
 296                 return false;
 297
 298         /*
 299          * If state is UNUSED at least show the pointer requested; the rest
 300          * would be garbage data.
 301          */
 302         kpp->kp_ptr = object;
 303
 304         /* Requesting info an a never-used object is almost certainly a bug. */
 305         if (WARN_ON(meta->state == KFENCE_OBJECT_UNUSED))
 306                 return true;
 307
 308         raw_spin_lock_irqsave(&meta->lock, flags);
 309
 310         kpp->kp_slab = slab;
 311         kpp->kp_slab_cache = meta->cache;
 312         kpp->kp_objp = (void *)meta->addr;
 313         kfence_to_kp_stack(&meta->alloc_track, kpp->kp_stack);
 314         if (meta->state == KFENCE_OBJECT_FREED)
 315                 kfence_to_kp_stack(&meta->free_track, kpp->kp_free_stack);
 316         /* get_stack_skipnr() ensures the first entry is outside allocator. */
 317         kpp->kp_ret = kpp->kp_stack[0];
 318
 319         raw_spin_unlock_irqrestore(&meta->lock, flags);
 320
 321         return true;
 322 }
 323 #endif